Porcelain composition for varistor and varistor

ABSTRACT

A varistor is provided which can be driven at a low voltage, has a small leak current, and can realize a high ESD resistance and a high surge resistance. The varistor is formed using a ceramic composition for a varistor which contains zinc oxide as a primary component and sub-components including praseodymium at a content of 0.05 to 3.0 atomic percent of the total, cobalt at a content of 0.5 to 10 atom percent of the total, at least one of potassium, sodium, and lithium at a total content of 0.005 to 0.5 atom percent of the total, at least one of aluminum, gallium, and indium at a total content of 2×10 −5  to 0.5 atom percent of the total, and zirconium at a content of 0.005 to 5.0 atom percent of the total.

TECHNICAL FIELD

The present invention relates to ceramic compositions for varistors usedfor electrostatic protection elements, noise filters, and the like andto the varistors, and more particularly, relates to a ceramiccomposition for a varistor primarily composed of ZnO and the varistor.

BACKGROUND ART

Heretofore, for protection against overvoltage, varistors having amonolayer sintered body primarily composed of ZnO have been widely used.In recent years, in addition to the protection against overvoltage, aselectrostatic discharge (ESD) protection elements and noise filters,multilayer varistors composed of a plurality of internal electrodesdisposed in a sintered body have been increasingly used.

In addition, concomitant with the trend toward higher integration andlower drive voltage of electronic apparatuses such as mobilecommunication apparatuses and notebook personal computers, varistorshave been strongly required to be stably driven at a lower rated voltageand to have superior reliability.

In electronic apparatuses, ESD may occur frequently at interfaceportions with the exterior, and as elements for protecting interiordevices, a great number of Zener diodes and chip type varistors havebeen widely used. The chip type varistors have no polarity incurrent-voltage characteristics (I-V characteristics) and havebi-directional characteristics. Accordingly, as compared to SMD typeZener diodes incorporating two elements, when the chip type varistorsare used, reduction in cost and reduction in mounting area can beachieved.

Incidentally, the threshold voltage (hereinafter referred to as“varistor voltage”) of varistors using a sintered body primarilycomposed of ZnO is proportional to the number of grain boundariespresent between electrodes. It has been believed that the varistorvoltage per one grain boundary is between 2 to 3 V. Accordingly, inorder to form a varistor to be driven at a low voltage of 30 V or less,the number of grain boundaries present between electrodes must be notmore than ten and several.

As a method for decreasing the number of grain boundaries betweenelectrodes, there may be mentioned a method for decreasing the thicknessof a characteristic layer (that is, the varistor layer) to decrease thenumber of grain boundaries and a method for increasing the graindiameter to decrease the number of grain boundaries. In the method fordecreasing the thickness of a characteristic layer, due to the presenceof pin holes or the variation in thickness of green sheets, which aresheets before a sintering step is performed for forming thecharacteristic layer, the properties may significantly vary in somecases, and in addition, grain strength may be decreased in some cases.On the other hand, in the method for increasing the grain diameter, thegrowth of grains must be facilitated, and hence abnormal growth ofgrains is liable to occur, thereby increasing the variation in graindiameter. As a result, the variation in properties may be increased insome cases.

Accordingly, when a multilayer varistor to be driven at a low voltage isformed, in order to maintain element strength and to decrease thevariation in properties, the sintered body layer present betweeninternal electrodes, that is, the characteristic layer must have athickness at a certain level or more, and in addition, the variation ingrain diameter must be decreased.

A varistor material primarily composed of ZnO is generally categorizedinto a material containing a Bi base sub-component formed of Bi₂O₃,Sb₂O₃, CoO, MnO, and the like disclosed, for example, in JapaneseExamined Patent Application Publication No. 53-11076 and a materialcontaining a Pr base sub-component formed of Pr₆O₁₁, CoO, and the likedisclosed, for example, in Japanese Examined Patent ApplicationPublication No. 56-11076.

By the use of the barrister material containing a Bi base sub-component,a varistor suitably used for overvoltage protection for a large currentapplication can be easily supplied at a relatively low cost. However, infiring, Bi₂O₃ or Sb₂O₃ having a low melting point tended to form aliquid phase and was also liable to evaporate. As a result, it wasdifficult to decrease the variation in grain diameter. Accordingly, whenthe number of grain boundaries was decreased for realizing a lower drivevoltage, the variation in properties was inevitably increased due to thevariation in grain diameter. Consequently, it has been difficult tostably manufacture and supply multilayer varistors which can be drivenat a lower voltage and which has superior reliability. In addition,since the variation in grain diameter was liable to increase, a surgecurrent or ESD was concentrated at positions at which grains having alarge grain diameter were present, and the resistances against surgecurrent and ESD were also liable to decrease.

On the other hand, in the varistor material containing a Pr basesub-component, Bi₂O₃ and Sb₂O₃ are not contained which form a liquidphase at a low temperature and which are liable to evaporate.Accordingly, varistors having stable and superior properties can bemanufactured in mass production and can be supplied. However, ascompared to the varistor material containing a Bi base sub-component,the varistor material containing a Pr base sub-component had a problemof a large leak current. In order to realize a lower drive voltage, whenthe thickness of the characteristic layer is decreased, the leak currentis further increased, and the insulation resistance and the voltagenon-linearity are degraded. Hence, there have been problems in that thepower consumption is increased and that the malfunction of signalcircuits occurs. In order to decrease the leak current, it is effectivethat the donor concentration in ZnO grains be decreased or that a largeramount of an insulating material be added. However, when the methodsdescribed above are used, the surge resistant is significantlydecreased.

When a conventional varistor material containing a Pr base sub-componentis used, in a multilayer chip type varistor which can be driven at a lowvoltage of 30 V or less, it has been difficult to suppress the leakcurrent and to realize a high surge resistance.

In Japanese Unexamined Patent Application Publication No. 7-29709, avoltage non-linear resistor has been disclosed which can be driven at alow voltage and which has a high surge resistance and a large resistanceagainst electrostatic discharge. In this technique, a voltage non-linearresistor has been disclosed having a composition containing ZnO as aprimary component, and Pr₆O₁₁, Bi₂O₃, Mn₃O₄, and CoO as sub-components.However, since Bi₂O₃ tends to form a liquid phase at a low temperatureor is liable to evaporate, it has been difficult to obtain uniformparticle diameters. In addition, it has also been difficult to stablysupply a voltage non-linear resistor which has superior reliability andwhich can be driven at a low voltage.

In consideration of the present situation of the conventional techniquesdescribed above, an object of the present invention is to obtain aceramic composition for a varistor and the varistor, the ceramiccomposition capable of forming a highly reliable varistor which can bestably driven at a low voltage and which has a small leak current, ahigh surge resistance, and a large ESD resistance.

DISCLOSURE OF INVENTION

A ceramic composition for a varistor, according to the presentinvention,.comprises: zinc oxide as a primary component; andsub-components including praseodymium at a content of 0.05 to 3.0 atomicpercent of the total, cobalt at a content of 0.5 to 10 atom percent ofthe total, at least one of potassium, sodium, and lithium at a totalcontent of 0.005 to 0.5 atom percent of the total, at least one ofaluminum, gallium, and indium at a total content of 2×10⁻⁵ to 0.5 atompercent of the total, and zirconium at a content of 0.005 to 5.0 atompercent of the total.

A varistor of the present invention comprises a sintered body and aplurality of terminal electrodes formed on exterior surfaces of thesintered body, the sintered body having a ceramic composition which isused for forming a varistor and which has the above specificcomposition. The structure thereof is not particularly limited. That is,there may be provided a monolayer varistor composed of a monolayervaristor substrate of the sintered body described above and exteriorelectrodes provided on two surfaces thereof. However, in accordance withone specific aspect of the present invention, in the sintered bodydescribed above, a plurality of interior electrodes is formed to belaminated to each other with sintered body layers provided therebetween,and the interior electrodes mentioned above are electrically connectedto respective exterior electrodes, thereby forming a multilayervaristor. Hence, in particular, a multilayer varistor can be providedwhich can be driven at a low voltage, such as at a rated voltage of 30 Vor less, and which has a small leak current, a high surge resistance, asufficiently large ESD resistance, and superior reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing the structure of amultilayer varistor according to one example of the present invention.

FIG. 2 is a schematic, exploded, perspective view of a laminate used forthe multilayer varistor sown in FIG. 1.

FIG. 3 is a graph showing a surge waveform used for a surge test.

FIG. 4 is a graph showing an ESD waveform used for an ESD resistancetest.

FIG. 5 is a graph showing the relationship of the Zr content with theESD resistance and the initial insulation resistance of a varistor at avaristor voltage of 9 V.

FIG. 6 is a graph showing the relationship of the Zr content with theESD resistance and the initial insulation resistance of a varistor at avaristor voltage of 12 V.

FIG. 7 is a graph showing the relationship of the Zr content with theESD resistance and the initial insulation resistance of a varistor at avaristor voltage of 27 V.

BEST MODE FOR CARRYING OUT THE INVENTION

In the ceramic composition for a varistor, according to the presentinvention, as a sub-component, at least one of calcium, strontium, andbarium is preferably further contained at a total content of 1.0 atompercent or less of the total. In this case, the insulation resistance IRcan be further increased.

In the present invention, as a sub-component, at least one of lanthanum,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, thulium, ytterbium, and yttrium is preferably further containedat a total content of 1.0 atom percent or less of the total. In thiscase, the surge resistance can be further improved.

In the present invention, the zirconium is preferably contained at acontent of 0.01 to 5.0 atom percent of the total, and in this case, evenwhen the varistor voltage is lower, a large ESD resistance can beobtained.

The zirconium is more preferably contained at a content of 0.05 to 5.0atom percent of the total, and even at a lower working voltage, asufficient ESD resistance can be obtained.

In the ceramic composition for a varistor, according to the presentinvention, the reason the content of praseodymium (Pr) is set in therange of from 0.05 to 3.0 atom percent is that when the content is lessthan 0.05 atom percent, the supply amount of oxygen from Pr₆G₁₁ isdecreased, and the initial insulation resistance and the ESD resistanceare decreased. On the other hand, when the content is more than 3.0 atompercent, Pr₆O₁₁ segregates primarily in the grain boundaries, and thevariation in grain diameter is increased. Consequently, current or anelectric field is locally concentrated, and hence the surge resistanceand the ESD resistance are decreased.

The reasons the content of Co is set in the range of from 0.5 to 10 atompercent are as follows. When the content is less than 0.5 atom percent,the density at the boundary level is decreased, and the initialinsulation resistance and the ESD resistance are decreased. On the otherhand, when the content is more than 10 atom percent, since Co is nottotally dissolved in ZnO and segregates in the grain boundaries, theelectron conduction is decreased, and the surge resistance and the ESDresistance are decreased.

The reasons the total content of at least one of potassium (K), sodium(Na), and lithium (Li) is set in the range of from 0.005 to 0.5 atompercent are as follows. When the content is less than 0.005 atompercent, K, Na, and/or Li cannot insulate all the grain boundaries, andas a result, the initial insulation resistance is decreased. When thecontent is more than 0.5 atom percent, since K, Na, and/or Li isexcessively dissolved in ZnO, the resistance in the grains is increased,and the surge resistance and the ESD resistance are decreased.

The reasons the total content of at least one of aluminum (Al), gallium(Ga), and indium (In) is set in the range of from 2×10⁻⁵ to 0.5 atompercent are as follows. When the content is less than 2×10⁻⁵ atompercent, the resistance in the grains is excessively increased, and thesurge resistance and the ESD resistance are decreased. When the contentis more than 0.5 atom percent, the resistance in the grains isexcessively decreased, and the initial insulation resistance isdecreased.

The reasons the content of zirconium (Zr) is set in the range of from0.005 to 5.0 atom percent are as follows. When the content is less than0.005 atom percent, abnormal grain growth cannot be suppressed, thevariation in grain diameter cannot be controlled, and the reduction indefective grain boundaries cannot be achieved. As a result, the surgeresistance and the ESD resistance are decreased. When the content ismore than 5.0 atom percent, since ZrO₂ segregates primarily in the grainboundaries, although the insulation resistance is improved, thesintering properties are degraded, and the surge resistance and the ESDresistance are decreased.

The reason the total content of at least one of calcium (Ca), strontium(Sr), and barium (Ba) is preferably set to 1.0 atom percent or less isas follows. When the content is more than 1.0 atom percent, since thesegregation thereof excessively occurs in the grain boundaries, theelectron conduction is decreased, the insulation resistance may beincreased in some cases, and the surge resistance and the ESD resistancemay be decreased in some cases.

In addition, in the present invention, the total content of at least oneof lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb), and yttrium (Y) is preferably set to1.0 atom percent or less and more preferably set in the range of from0.01 to 0.5 atom percent. When lanthanum is contained, the surgeresistance can be more effectively enhanced.

EXAMPLES

Hereinafter, the present invention will be described with reference toparticular examples.

Example 1

In Example 1, among Pr, Co, K, Al, and Zr used as a sub-component,samples in which the content of Pr was primarily changed were formed,and the properties thereof were evaluated.

First, ZnO, Pr₆O₁₁, CoO, K₂CO₃, Al₂O₃, and ZrO₂ powders used as startingmaterials were weighed so that a ceramic sintered body after firing hada predetermined composition and were then wet-mixed by a ball mill for24 hours, thereby forming a mixed slurry. After dehydrated and dried,the mixed slurry was calcined at a temperature of 700 to 1,100° C. for 2hours in the air, thereby forming a calcined raw material. The calcinedraw material thus obtained was again sufficiently pulverized using aball mill, and subsequently, dehydration and drying were performed. Anorganic binder, an organic plasticizer, and a dispersing agent wereadded to the raw material thus dried, and a mixture thus formed wasmixed for 12 hours using a ball mill, thereby forming a slurry.

The slurry thus formed was processed on a PET film by a doctor blademethod to form a green sheet 25 μm thick. The green sheet thus preparedwas cut into a rectangular shape.

Next, a Pt paste was screen-printed on the rectangular ceramic greensheet, thereby forming an internal electrode pattern. A plurality ofceramic green sheets having internal electrode patterns printed thereonwas laminated, and plain ceramic green sheets were provide on the topand the bottom of the laminate thus formed, thereby forming a motherlaminate.

The mother laminate thus formed was pressed at a pressure of 1.96×10⁸ Paand was then cut into laminates each having a size for forming avaristor. As described above, a laminate 1 schematically shown in anexploded perspective view of FIG. 2 was obtained. In the laminate 1,ceramic green sheets 4 and 5 provided with internal electrodes 2 and 3,respectively, were alternately laminated to each other in the laminationdirection. That is, the ceramic green sheets 4 and 5 are laminated toeach other so that the end surfaces of the internal electrodes 2 and 3are alternately disposed at the sides opposite to each other in thelamination direction. In this laminate, reference numeral 6 indicates aplain ceramic green sheet.

In the laminate 1 obtained as described above, the number of thelaminated internal electrodes was set to 10, the overlapping areabetween the internal electrodes was set to 2.3 mm², the length of thelaminate was set to 1.6 mm, the width was set to 0.8 mm, and thethickness was set to 0.8 mm.

The laminate 1 thus obtained was heated to 500° C. for 12 hours in theair, thereby removing the organic binder. Subsequently, firing wasperformed at 1,150 to 1,250° C. for 2 hours in the air, thereby forminga ceramic sintered body.

As shown in FIG. 1, an Ag paste was applied onto two end surfaces 7 aand 7 b of a sintered body 7 thus formed, followed by firing at atemperature of 800° C. in the air, so that exterior electrodes 8 and 9were formed, and hence a multilayer varistor 10 was formed.

Next, the following measurement was performed for the multilayervaristor thus formed. That is, (1) varistor voltage (V_(1mA)), (2)initial insulation resistance (IR) obtained when 60% of the varistorvoltage was applied for 0.1 second, (3) surge resistance, and (4) ESDresistance were measured. For the evaluation of the surge resistance,the varistor voltage was obtained after a triangle electrical waveformof 8×20 μs shown in FIG. 3 was applied twice at an interval of 5minutes, and when the ratio of the rate of change of varistor voltage,ΔV_(1mA), to the initial varistor voltage V_(1mA), that is, whenΔV_(1mA)/V_(1mA) was within 10%, and when the change of IR, that is,when Δlog IR was within ½, the maximum current wave height was measured.For the evaluation of the ESD resistance, after an ESD pulse inaccordance with IEC801-2 shown in FIG. 4 was applied 10 times from apair of exterior electrodes of each multilayer varistor, when the rateof change of varistor voltage, ΔV_(1mA)/V_(1mA), was within 10%, andwhen the change of IR, Δlog IR, was within ½, the maximum applicationvoltage was measured.

The results are shown in the following Table 1. In addition, in Table 1,the compositions of the sintered bodies of the individual varistorsformed in Example 1 are also shown.

In the following tables, the samples provided with asterisks are sampleseach contain zinc oxide as a primary component and sub-componentsincluding praseodymium at a content of 0.05 to 3.0 atomic percent of thetotal, cobalt at a content of 0.5 to 10 atom percent of the total, atleast one of potassium, sodium, and lithium at a total content of 0.005to 0.5 atom percent of the total, at least one of aluminum, gallium, andindium at a total content of 2×10⁻⁵ to 0.5 atom percent of the total,and zirconium at a content of 0.005 to 5.0 atom percent of the total.TABLE 1 SURGE ESD SAMPLE ADDITION ELEMENT (atom %) VARISTOR RESIS-RESIS- NO. Pr Co K Al Zr INITIAL IR VOLTAGE TANCE TANCE * 1 0 2.0 0.05 1× 10⁻⁴ 0.1 0.05 MΩ 8.8 V 15 A 2 kV * 2 0.01 2.0 0.05 1 × 10⁻⁴ 0.1 0.15MΩ 9.1 V 17 A 2 kV * 3 0.03 2.0 0.05 1 × 10⁻⁴ 0.1 0.5 MΩ 9.0 V 17 A 5 kV4 0.05 2.0 0.05 1 × 10⁻⁴ 0.1 1.0 MΩ 8.7 V 20 A 30 kV 5 0.1 2.0 0.05 1 ×10⁻⁴ 0.1 1.6 MΩ 9.1 V 20 A 30 kV 6 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 1.8 MΩ 9.4V 25 A 30 kV 7 0.5 2.0 0.05 1 × 10⁻⁴ 0.1 3.2 MΩ 9.2 V 21 A 30 kV 8 1 2.00.05 1 × 10⁻⁴ 0.1 3.5 MΩ 8.8 V 20 A 30 kV 9 3 2.0 0.05 1 × 10⁻⁴ 0.1 4.1MΩ 9.4 V 20 A 30 kV * 10 5 2.0 0.05 1 × 10⁻⁴ 0.1 7.5 MΩ 9.4 V 17 A 15kV * 11 6 2.0 0.05 1 × 10⁻⁴ 0.1 8.2 MΩ 9.0 V 14 A 5 kV 12 3 0.5 0.05 1 ×10⁻⁴ 0.1 2.1 MΩ 8.8 V 20 A 30 kV 13 0.05 10.0 0.05 1 × 10⁻⁴ 0.1 2.3 MΩ9.0 V 22 A 30 kV 14 3 10.0 0.05 1 × 10⁻⁴ 0.1 5.8 MΩ 8.9 V 20 A 30 kV 150.05 2.0 0.5 1 × 10⁻⁴ 0.1 3.9 MΩ 9.1 V 21 A 30 kV 16 3 2.0 0.005 1 ×10⁻⁴ 0.1 2.0 MΩ 9.0 V 25 A 30 kV 17 3 2.0 0.5 1 × 10⁻⁴ 0.1 4.2 MΩ 9.2 V21 A 30 kV 18 0.05 2.0 0.05 2 × 10⁻⁵ 0.1 3.1 MΩ 9.0 V 22 A 30 kV 19 32.0 0.05 2 × 10⁻⁵ 0.1 5.3 MΩ 8.7 V 20 A 30 kV 20 3 2.0 0.05 0.5 0.1 1.3MΩ 9.1 V 27 A 30 kV 21 0.05 2.0 0.05 1 × 10⁻⁴ 0.05 1.1 MΩ 9.0 V 24 A 30kV 22 0.05 2.0 0.05 1 × 10⁻⁴ 5 1.9 MΩ 9.1 V 21 A 30 kV 23 3 2.0 0.05 1 ×10⁻⁴ 0.05 2.8 MΩ 9.0 V 22 A 30 kV 24 3 2.0 0.05 1 × 10⁻⁴ 5 4.1 MΩ 9.1 V20 A 30 kV

As can be seen from Table 1, according to sample Nos. 1 to 3, since thePr content was less than 0.05 atom percent, the initial IR, the surgeresistance, and the ESD resistance were low. According to sample Nos. 10and 11, since the Pr content was more than 3.0 atom percent, althoughthe initial IR was high, the surge resistance and the ESD resistancewere low.

On the other hand, according to sample Nos. 4 to 9 and 12 to 24, sincethe Pr content was in the range of from 0.05 to 3.0 atom percent, verysuperior properties could be obtained, that is, the varistor voltage waslow, such as approximately 9 V, the initial insulation resistance IR was1.0 MΩ or more, the surge resistance was 20 A or more, and in addition,the ESD resistance was 30 kV. Accordingly, since a sample having a Prcontent in the range of from 0.05 to 3.0 atom percent was used, in achip type varistor designed to cooperate with a circuit driven at a lowvoltage, such as a rated voltage of 30 V or less, the leak current couldbe decreased, and a high surge resistance and a high ESD resistancecould be realized.

Example 2

In Example 2, among Pr, Co, K, Al, and Zr used as a sub-component,samples in which the content of Co was primarily changed were formed,and the properties thereof were evaluated.

Except that the contents of the sub-components were changed as shown inthe following Table 2, multilayer varistors were formed in the samemanner as that in Example 1, and the evaluation was performed. Theresults are shown in Table 2 below. TABLE 2 SURGE ESD SAMPLE ADDITIONELEMENT (atom %) VARISTOR RESIS- RESIS- NO. Pr Co K Al Zr INITIAL IRVOLTAGE TANCE TANCE * 25 0.3 0.1 0.05 1 × 10⁻⁴ 0.1 0.04 MΩ 9.1 V 15 A 2kV * 26 0.3 0.3 0.05 1 × 10⁻⁴ 0.1 0.5 MΩ 9.0 V 18 A 5 kV 27 0.3 0.5 0.051 × 10⁻⁴ 0.1 1.0 MΩ 8.8 V 20 A 30 kV 28 0.3 1 0.05 1 × 10⁻⁴ 0.1 1.6 MΩ8.9 V 20 A 30 kV 29 0.3 2 0.05 1 × 10⁻⁴ 0.1 1.8 MΩ 9.4 V 25 A 30 kV 300.3 4 0.05 1 × 10⁻⁴ 0.1 2.5 MΩ 9.1 V 21 A 30 kV 31 0.3 5 0.05 1 × 10⁻⁴0.1 2.7 MΩ 9.2 V 21 A 30 kV 32 0.3 8 0.05 1 × 10⁻⁴ 0.1 3.2 MΩ 9.0 V 20 A30 kV 33 0.3 10 0.05 1 × 10⁻⁴ 0.1 4.1 MΩ 8.9 V 20 A 30 kV * 34 0.3 120.05 1 × 10⁻⁴ 0.1 6.0 MΩ 8.8 V 18 A 15 kV 35 0.3 0.5 0.5 1 × 10⁻⁴ 0.12.3 MΩ 8.8 V 21 A 30 kV 36 0.3 10 0.005 1 × 10⁻⁴ 0.1 3.9 MΩ 8.9 V 23 A30 kV 37 0.3 10 0.5 1 × 10⁻⁴ 0.1 5.3 MΩ 9.1 V 20 A 30 kV 38 0.3 0.5 0.052 × 10⁻⁵ 0.1 1.0 MΩ 9.5 V 21 A 30 kV 39 0.3 10 0.05 2 × 10⁻⁵ 0.1 4.5 MΩ8.7 V 20 A 30 kV 40 0.3 10 0.05 0.5 0.1 2.3 MΩ 9.0 V 29 A 30 kV 41 0.30.5 0.05 1 × 10⁻⁴ 5 2.1 MΩ 8.7 V 20 A 30 kV 42 0.3 10 0.05 1 × 10⁻⁴ 0.055.6 MΩ 8.8 V 23 A 30 kV 43 0.3 10 0.05 1 × 10⁻⁴ 5 6.2 MΩ 9.3 V 20 A 30kV

As can be seen from Table 2, according to sample Nos. 25 and 26, sincethe Co content was less than 0.5 atom percent, the initial IR and theESD resistance were low. According to sample No. 34, since the Cocontent was more than 10 atom percent, although the initial IR was high,the surge resistance and the ESD resistance were low.

On the other hand, according to sample Nos. 27 to 33 and 35 to 43, sincethe Co content was set in the range of from 0.5 to 10 atom percent,although the varistor voltage was low, such as approximately 9 V, theinitial insulation resistance IR was 1.0 MΩ or more, the surgeresistance was 20 A or more, and the ESD resistance was 30 kV.

Accordingly, since the content of Co was set in the range of from 0.5 to10 atom percent, in a multilayer varistor designed to cooperate with acircuit driven at a low voltage, such as a rated voltage of 30 V orless, it was understood that the leak current could be decreased, and ahigh surge resistance and a high ESD resistance could be realized.

Example 3

In Example 3, among Pr, Co, K, Al, and Zr used as a sub-component,samples in which the content of K was primarily changed were formed, andthe properties thereof were evaluated.

Except that the contents of the sub-components were changed as shown inthe following Table 2, multilayer varistors were formed in the samemanner as that in Example 1, and the evaluation was performed. Theresults are shown in Table 3 below. TABLE 3 SURGE ESD SAMPLE ADDITIONELEMENT (atom %) VARISTOR RESIS- RESIS- NO. Pr Co K Al Zr INITIAL IRVOLTAGE TANCE TANCE * 44 0.3 2.0 0 1 × 10⁻⁴ 0.1 0.001 MΩ 8.7 V 30 A 30kV * 45 0.3 2.0 0.001 1 × 10⁻⁴ 0.1 0.02 MΩ 8.9 V 29 A 30 kV * 46 0.3 2.00.003 1 × 10⁻⁴ 0.1 0.4 MΩ 9.2 V 29 A 30 kV 47 0.3 2.0 0.005 1 × 10⁻⁴ 0.11.0 MΩ 9.0 V 27 A 30 kV 48 0.3 2.0 0.01 1 × 10⁻⁴ 0.1 1.4 MΩ 9.2 V 26 A30 kV 49 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 1.8 MΩ 9.4 V 25 A 30 kV 50 0.3 2.00.08 1 × 10⁻⁴ 0.1 2.2 MΩ 8.9 V 25 A 30 kV 51 0.3 2.0 0.1 1 × 10⁻⁴ 0.12.9 MΩ 9.0 V 24 A 30 kV 52 0.3 2.0 0.3 1 × 10⁻⁴ 0.1 3.2 MΩ 9.1 V 20 A 30kV 53 0.3 2.0 0.5 1 × 10⁻⁴ 0.1 3.4 MΩ 9.0 V 20 A 30 kV * 54 0.3 2.0 0.81 × 10⁻⁴ 0.1 4.2 MΩ 8.8 V 15 A 15 kV * 55 0.3 2.0 1 1 × 10⁻⁴ 0.1 6.0 MΩ8.9 V 11 A 5 kV 56 0.3 2.0 0.005 2 × 10⁻⁵ 0.1 1.5 MΩ 9.1 V 25 A 30 kV 570.3 2.0 0.005 0.5 0.1 1.1 MΩ 9.3 V 33 A 30 kV 58 0.3 2.0 0.5 2 × 10⁻⁵0.1 3.7 MΩ 8.7 V 20 A 30 kV 59 0.3 2.0 0.5 0.5 0.1 2.0 MΩ 9.0 V 29 A 30kV 60 0.3 2.0 0.005 1 × 10⁻⁴ 0.05 1.2 MΩ 9.1 V 26 A 30 kV 61 0.3 2.00.005 1 × 10⁻⁴ 5 3.3 MΩ 9.2 V 21 A 30 kV 62 0.3 2.0 0.5 1 × 10⁻⁴ 0.053.2 MΩ 9.1 V 24 A 30 kV 63 0.3 2.0 0.5 1 × 10⁻⁴ 5 4.9 MΩ 9.3 V 20 A 30kV

As can be seen from Table 3, according to sample Nos. 44 to 46, sincethe K content was less than 0.005 atom percent, the initial IR was low,and according to sample Nos. 54 and 55, since the K content was morethan 0.5 atom percent, although the initial IR was high, the surgeresistance and the ESD resistance were low.

On the other hand, according to sample Nos. 47 to 53 and 56 to 63, sincethe K content was set in the range of from 0.005 to 0.5 atom percent,although the varistor voltage was low, such as approximately 9 V, theinitial IR was 1.0 MΩ or more, the surge resistance was 20 A or more,and the ESD resistance was 30 kV.

Accordingly, since the content of K was set in the range of from 0.005to 0.5 atom percent, in a multilayer varistor designed to cooperate witha circuit driven at a low voltage, such as a rated voltage of 30 V orless, it was understood that the leak current could be decreased, and ahigh surge resistance and a high ESD resistance could be realized.

Subsequently, as shown in the following Tables 4 to 6, instead of K,samples containing Na or Li, and samples containing K, Na, and/or Liwhich were optionally combined with each other were evaluated in thesame manner as that in Example 3 described above. TABLE 4 SURGE ESDSAMPLE ADDITION ELEMENT (atom %) VARISTOR RESIS- RESIS- NO. Pr Co Na AlZr INITIAL IR VOLTAGE TANCE TANCE * 64 0.3 2.0 0.001 1 × 10⁻⁴ 0.1 0.1 MΩ9.1 V 29 A 30 kV 65 0.3 2.0 0.005 1 × 10⁻⁴ 0.1 1.1 MΩ 9.3 V 29 A 30 kV66 0.3 2.0 0.01 1 × 10⁻⁴ 0.1 1.8 MΩ 9.0 V 27 A 30 kV 67 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 2.9 MΩ 8.8 V 27 A 30 kV 68 0.3 2.0 0.08 1 × 10⁻⁴ 0.1 3.3 MΩ 9.4V 24 A 30 kV 69 0.3 2.0 0.1 1 × 10⁻⁴ 0.1 4.1 MΩ 9.0 V 23 A 30 kV 70 0.32.0 0.3 1 × 10⁻⁴ 0.1 4.5 MΩ 9.0 V 22 A 30 kV 71 0.3 2.0 0.5 1 × 10⁻⁴ 0.14.9 MΩ 9.1 V 20 A 30 kV * 72 0.3 2.0 0.8 1 × 10⁻⁴ 0.1 6.3 MΩ 8.8 V 10 A30 kV 73 0.05 2.0 0.005 1 × 10⁻⁴ 0.1 1.3 MΩ 9.3 V 21 A 30 kV 74 0.05 2.00.5 1 × 10⁻⁴ 0.1 3.1 MΩ 9.0 V 20 A 30 kV 75 3 2.0 0.005 1 × 10⁻⁴ 0.1 3.8MΩ 9.1 V 22 A 30 kV 76 3 2.0 0.5 1 × 10⁻⁴ 0.1 5.6 MΩ 8.8 V 20 A 30 kV 770.3 0.5 0.5 1 × 10⁻⁴ 0.1 2.0 MΩ 9.0 V 21 A 30 kV 78 0.3 10.0 0.005 1 ×10⁻⁴ 0.1 3.8 MΩ 9.1 V 21 A 30 kV 79 0.3 10.0 0.5 1 × 10⁻⁴ 0.1 5.1 MΩ 9.3V 20 A 30 kV 80 0.3 2.0 0.005 2 × 10⁻⁵ 0.1 1.7 MΩ 9.0 V 24 A 30 kV 810.3 2.0 0.005 0.5 0.1 1.3 MΩ 9.0 V 30 A 30 kV 82 0.3 2.0 0.5 2 × 10⁻⁵0.1 4.0 MΩ 8.9 V 20 A 30 kV 83 0.3 2.0 0.5 0.5 0.1 2.5 MΩ 9.1 V 28 A 30kV 84 0.3 2.0 0.005 1 × 10⁻⁴ 0.05 1.4 MΩ 9.0 V 27 A 30 kV 85 0.3 2.00.005 1 × 10⁻⁴ 5 3.5 MΩ 8.8 V 22 A 30 kV 86 0.3 2.0 0.5 1 × 10⁻⁴ 0.053.1 MΩ 9.0 V 25 A 30 kV 87 0.3 2.0 0.5 1 × 10⁻⁴ 5 4.8 MΩ 9.1 V 21 A 30kV

TABLE 5 SURGE ESD SAMPLE ADDITION ELEMENT (atom %) VARISTOR RESIS-RESIS- NO. Pr Co Li Al Zr INITIAL IR VOLTAGE TANCE TANCE * 88 0.3 2.00.001 1 × 10⁻⁴ 0.1 0.5 MΩ 9.0 V 27 A 30 kV 89 0.3 2.0 0.005 1 × 10⁻⁴ 0.12.0 MΩ 8.9 V 25 A 30 kV 90 0.3 2.0 0.01 1 × 10⁻⁴ 0.1 2.3 MΩ 9.1 V 24 A30 kV 91 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 3.4 MΩ 8.8 V 23 A 30 kV 92 0.3 2.00.08 1 × 10⁻⁴ 0.1 4.2 MΩ 8.9 V 23 A 30 kV 93 0.3 2.0 0.1 1 × 10⁻⁴ 0.15.0 MΩ 9.1 V 22 A 30 kV 94 0.3 2.0 0.3 1 × 10⁻⁴ 0.1 5.5 MΩ 9.3 V 21 A 30kV 95 0.3 2.0 0.5 1 × 10⁻⁴ 0.1 6.0 MΩ 8.8 V 20 A 30 kV * 96 0:3 2.0 0.81 × 10⁻⁴ 0.1 6.4 MΩ 9.0 V 8 A 20 kV 97 0.05 2.0 0.005 1 × 10⁻⁴ 0.1 1.8MΩ 9.0 V 20 A 30 kV 98 0.05 2.0 0.5 1 × 10⁻⁴ 0.1 3.5 MΩ 8.8 V 21 A 30 kV99 3 2.0 0.005 1 × 10⁻⁴ 0.1 4.3 MΩ 8.8 V 20 A 30 kV 100 3 2.0 0.5 1 ×10⁻⁴ 0.1 5.9 MΩ 8.7 V 20 A 30 kV 101 0.3 0.5 0.5 1 × 10⁻⁴ 0.1 3.2 MΩ 8.8V 20 A 30 kV 102 0.3 10.0 0.005 1 × 10⁻⁴ 0.1 4.1 MΩ 8.9 V 20 A 30 kV 1030.3 10.0 0.5 1 × 10⁻⁴ 0.1 5.9 MΩ 8.8 V 20 A 30 kV 104 0.3 2.0 0.005 2 ×10⁻⁵ 0.1 2.0 MΩ 8.8 V 22 A 30 kV 105 0.3 2.0 0.005 0.5 0.1 1.6 MΩ 9.1 V29 A 30 kV 106 0.3 2.0 0.5 2 × 10⁻⁵ 0.1 4.1 MΩ 9.0 V 21 A 30 kV 107 0.32.0 0.5 0.5 0.1 3.3 MΩ 9.0 V 27 A 30 kV 108 0.3 2.0 0.005 1 × 10⁻⁴ 0.052.5 MΩ 8.9 V 26 A 30 kV 109 0.3 2.0 0.005 1 × 10⁻⁴ 5 3.7 MΩ 9.3 V 23 A30 kV 110 0.3 2.0 0.5 1 × 10⁻⁴ 0.05 3.9 MΩ 8.7 V 26 A 30 kV 111 0.3 2.00.5 1 × 10⁻⁴ 5 5.0 MΩ 9.0 V 20 A 30 kV

TABLE 6 ADDITION ELEMENT (atom %) SURGE ESD K, Na, Li INITIAL VARISTORRESIS- RESIS- SAMPLE TOTAL IR VOLTAGE TANCE TANCE NO. Pr Co Al ZrCONTENT K Na Li (MΩ) (V) (A) (kV) * 112 0.3 2.0 1 × 10⁻⁴ 0.1 0 0 0 00.001 8.7 30 30 * 113 0.3 2.0 1 × 10⁻⁴ 0.1 0.001 0.0005 0.0005 0 0.059.1 28 30 114 0.3 2.0 1 × 10⁻⁴ 0.1 0.005 0.003 0.001 0.001 1.2 9.0 28 30115 0.3 2.0 1 × 10⁻⁴ 0.1 0.01 0.005 0.002 0.003 2.5 9.1 27 30 116 0.32.0 1 × 10⁻⁴ 0.1 0.05 0.01 0.03 0.01 4.1 8.8 25 30 117 0.3 2.0 1 × 10⁻⁴0.1 0.08 0.05 0.02 0.01 5.2 8.7 24 30 118 0.3 2.0 1 × 10⁻⁴ 0.1 0.1 0.050.03 0.02 5.5 9.3 21 30 119 0.3 2.0 1 × 10⁻⁴ 0.1 0.3 0.1 0.1 0.1 5.4 9.120 30 120 0.3 2.0 1 × 10⁻⁴ 0.1 0.5 0.2 0.2 0.1 7.4 9.0 20 30 * 121 0.32.0 1 × 10⁻⁴ 0.1 0.8 0.4 0.2 0.2 8.8 8.8 11 10

As apparently shown in Table 4, when the content of Na was in the rangeof from 0.005. to 0.5 atom percent as was the case of K, as can be seenfrom the results obtained from sample Nos. 65 to 71 and 73 to 87,although the varistor voltage was low, such as approximately 9 V, theinitial IR was 1.0 MΩ or more, the surge resistance was 20 A or more,and the ESD resistance was 30 kV.

In addition, as can be seen from Table 5, since the Li content was inthe range of from 0.005 to 0.5 atom percent in sample Nos. 89 to 95 and97 to 111, as was the case described above, although the varistorvoltage was low, such as approximately 9 V, the initial IR was 1.0 MΩ ormore, the surge resistance was 20 A or more, and the ESD resistance was30 kV.

Furthermore, as can be seen from Table 6, when K, Na, and Li wereoptionally combined with each other, according to sample Nos. 114 to 120in which the total content thereof was in the range of from 0.005 to 0.5atom percent, as was the case described above, although the varistorvoltage was low, such as approximately 9 V, the initial IR was 1.0 MΩ ormore, the surge resistance was 20 A or more, and the ESD resistance was30 kV.

Accordingly, from the results shown in Tables 3 to 6, when at least oneof K, Na, and Li was contained at a total content in the range of from0.005 to 0.5 atom percent, in a multilayer varistor designed tocooperate with a circuit driven at a low voltage, such as a ratedvoltage of 30 V or less, it was understood that the leak current couldbe decreased, and a high surge resistance and a high ESD resistancecould be realized. In addition, even when the varistor voltage was low,such as approximately 9 V, it was understood that very superiorproperties could be obtained, that is, an initial IR of 1.0 MΩ or more,a surge resistance of 20 A or more, an ESD resistance of 30 kV could beobtained.

Example 4

In Example 4, among Pr, Co, K, Al, and Zr used as a sub-component,samples in which the content of Al was primarily changed were formed,and the properties thereof were evaluated.

Except that the contents of the sub-components were changed as shown inthe following Table 7, multilayer varistors were formed in the samemanner as that in Example 1, and the evaluation was performed. Theresults are shown in Table 7 below. TABLE 7 SURGE ESD SAMPLE ADDITIONELEMENT (atom %) VARISTOR RESIS- RESIS- NO. Pr Co K Al Zr INITIAL IRVOLTAGE TANCE TANCE * 122 0.3 2 0.05 0  0.1 12 MΩ 9.0 V 8 A 5 kV * 1230.3 2 0.05 1 × 10⁻⁵ 0.1 8 MΩ 9.1 V 15 A 15 kV 124 0.3 2 0.05 2 × 10⁻⁵0.1 4.2 MΩ 8.8 V 20 A 30 kV 125 0.3 2 0.05 1 × 10⁻⁴ 0.1 1.8 MΩ 8.7 V 25A 30 kV 126 0.3 2 0.05 5 × 10⁻⁴ 0.1 1.7 MΩ 9.3 V 27 A 30 kV 127 0.3 20.05 1 × 10⁻³ 0.1 1.3 MΩ 9.0 V 28 A 30 kV 128 0.3 2 0.05 5 × 10⁻³ 0.11.2 MΩ 9.1 V 30 A 30 kV 129 0.3 2 0.05 1 × 10⁻² 0.1 1.0 MΩ 9.1 V 31 A 30kV 130 0.3 2 0.05 5 × 10⁻² 0.1 1.0 MΩ 9.3 V 33 A 30 kV 131 0.3 2 0.050.5 0.1 1.0 MΩ 9.6 V 34 A 30 kV * 132 0.3 2 0.05 1  0.1 0.05 MΩ 8.8 V 34A 30 kV 133 0.3 2 0.05 5 × 10⁻⁵ 0.05 4.1 MΩ 8.7 V 20 A 30 kV 134 0.3 20.05 5 × 10⁻⁵ 5 5.5 MΩ 9.0 V 26 A 30 kV 135 0.3 2 0.05 0.5 0.05 1.0 MΩ9.5 V 31 A 30 kV 136 0.3 2 0.05 0.5 5 5.4 MΩ 9.0 V 26 A 30 kV

As can be seen from Table 7, according to sample Nos. 122 and 123, sincethe Al content was less than 2×10⁻⁵ atom percent, although the initialIR was high, the surge resistance and the ESD resistance were low, andaccording to sample No. 132, since the Al content was more than 0.5 atompercent, although the surge resistance and the ESD resistance were high,the initial IR was extremely low.

On the other hand, according to sample Nos. 124 to 131 and 133 to 136,since the Al content was set in the range of from 2×10⁻⁵ to 0.5 atompercent in accordance with the present invention, although the varistorvoltage was low, such as approximately 9 V, the initial IR was 1.0 MΩ ormore, the surge resistance was 20 A or more, and the ESD resistance was30 kV.

Accordingly, since the content of Al was set in the range of from 2×10⁻⁵to 0.5 atom percent, in a multilayer varistor designed to cooperate witha circuit driven at a low voltage, such as a rated voltage of 30 V orless, it was understood that the leak current could be decreased, and ahigh surge resistance and a high ESD resistance could be realized.

Subsequently, instead of Al, samples containing Ga or In, and samples inwhich Al, Ga, and Li were optionally combined with each other were usedfor forming multilayer varistors in the same manner as that in Example 1described above, and the evaluation thereof was then performed. Thecompositions of the sub-components and the evaluation results are shownin Tables 8 to 10. TABLE 8 SURGE ESD SAMPLE ADDITION ELEMENT (atom %)VARISTOR RESIS- RESIS- NO. Pr Co K Ga Zr INITIAL IR VOLTAGE TANCETANCE * 137 0.3 2 0.05 1 × 10⁻⁶ 0.1 9.2 MΩ 8.8 V 12 A 20 kV 138 0.3 20.05 2 × 10⁻⁵ 0.1 5.3 MΩ 9.0 V 20 A 30 kV 139 0.3 2 0.05 1 × 10⁻⁴ 0.12.5 MΩ 9.1 V 21 A 30 kV 140 0.3 2 0.05 1 × 10⁻³ 0.1 2.1 MΩ 9.1 V 25 A 30kV 141 0.3 2 0.05 1 × 10⁻² 0.1 1.5 MΩ 8.9 V 27 A 30 kV 142 0.3 2 0.05 5× 10⁻² 0.1 1.1 MΩ 9.3 V 27 A 30 kV 143 0.3 2 0.05 0.5 0.1 1.1 MΩ 9.2 V28 A 30 kV * 144 0.3 2 0.05 1  0.1 0.5 MΩ 8.9 V 28 A 30 kV 145 0.05 20.05 2 × 10⁻⁵ 0.1 3.5 MΩ 9.1 V 22 A 30 kV 146 3 2 0.05 2 × 10⁻⁵ 0.1 5.4MΩ 8.9 V 21 A 30 kV 147 3 2 0.05 0.5 0.1 1.6 MΩ 9.0 V 25 A 30 kV 148 0.30.5 0.05 2 × 10⁻⁵ 0.1 1.5 MΩ 9.3 V 20 A 30 kV 149 0.3 10 0.05 2 × 10⁻⁵0.1 4.9 MΩ 9.0 V 21 A 30 kV 150 0.3 10 0.05 0.5 0.1 2.5 MΩ 9.1 V 28 A 30kV 151 0.3 2 0.005 2 × 10⁻⁵ 0.1 1.9 MΩ 9.0 V 24 A 30 kV 152 0.3 2 0.5 2× 10⁻⁵ 0.1 1.3 MΩ 9.2 V 30 A 30 kV 153 0.3 2 0.005 0.5 0.1 3.5 MΩ 9.0 V20 A 30 kV 154 0.3 2 0.5 0.5 0.1 2.9 MΩ 8.9 V 27 A 30 kV 155 0.3 2 0.052 × 10⁻⁵ 0.05 4.6 MΩ 8.8 V 21 A 30 kV 156 0.3 2 0.05 2 × 10⁻⁵ 5 5.5 MΩ8.9 V 25 A 30 kV 157 0.3 2 0.05 0.5 0.05 1.2 MΩ 9.3 V 28 A 30 kV 158 0.32 0.05 0.5 5 5.5 MΩ 9.1 V 24 A 30 kV

TABLE 9 SURGE ESD SAMPLE ADDITION ELEMENT (atom %) VARISTOR RESIS-RESIS- NO. Pr Co K In Zr INITIAL IR VOLTAGE TANCE TANCE * 159 0.3 2 0.051 × 10⁻⁶ 0.1 9.2 MΩ 9.1 V 11 A 15 kV 160 0.3 2 0.05 2 × 10⁻⁵ 0.1 5.3 MΩ9.0 V 20 A 30 kV 161 0.3 2 0.05 1 × 10⁻⁴ 0.1 2.5 MΩ 8.8 V 20 A 30 kV 1620.3 2 0.05 1 × 10⁻³ 0.1 2.1 MΩ 8.9 V 24 A 30 kV 163 0.3 2 0.05 1 × 10⁻²0.1 1.5 MΩ 8.7 V 26 A 30 kV 164 0.3 2 0.05 5 × 10⁻² 0.1 1.1 MΩ 9.2 V 28A 30 kV 165 0.3 2 0.05 0.5 0.1 1.0 MΩ 9.0 V 28 A 30 kV * 166 0.3 2 0.051  0.1 0.3 MΩ 9.0 V 27 A 30 kV 167 0.05 2 0.05 2 × 10⁻⁵ 0.1 4.0 MΩ 9.1 V21 A 30 kV 168 3 2 0.05 2 × 10⁻⁵ 0.1 5.5 MΩ 9.1 V 22 A 30 kV 169 3 20.05 0.5 0.1 1.9 MΩ 9.0 V 26 A 30 kV 170 0.3 0.5 0.05 2 × 10⁻⁵ 0.1 2.0MΩ 9.2 V 20 A 30 kV 171 0.3 10 0.05 2 × 10⁻⁵ 0.1 4.8 MΩ 8.9 V 22 A 30 kV172 0.3 10 0.05 0.5 0.1 2.6 MΩ 9.0 V 29 A 30 kV 173 0.3 2 0.005 2 × 10⁻⁵0.1 2.1 MΩ 8.8 V 23 A 30 kV 174 0.3 2 0.5 2 × 10⁻⁵ 0.1 1.2 MΩ 9.0 V 27 A30 kV 175 0.3 2 0.005 0.5 0.1 3.5 MΩ 9.1 V 21 A 30 kV 176 0.3 2 0.5 0.50.1 2.7 MΩ 8.8 V 26 A 30 kV 177 0.3 2 0.05 2 × 10⁻⁵ 0.05 4.5 MΩ 8.8 V 22A 30 kV 178 0.3 2 0.05 2 × 10⁻⁵ 5 5.4 MΩ 8.9 V 25 A 30 kV 179 0.3 2 0.050.5 0.05 1.1 MΩ 9.3 V 26 A 30 kV 180 0.3 2 0.05 0.5 5 5.9 MΩ 9.1 V 23 A30 kV

TABLE 10 ADDITION ELEMENT (atom %) SURGE ESD Al, Ga, In INITIAL VARISTORRESIS- RESIS- SAMPLE TOTAL IR VOLTAGE TANCE TANCE NO. Pr Co K Zr CONTENTAl Ga In (MΩ) (V) (A) (kV) * 181 0.3 2.0 0.05 0.1 0  0  0  0  12 9.0 85 * 182 0.3 2.0 0.05 0.1 1 × 10⁻⁵ 5 × 10⁻⁶ 2.5 × 10⁻⁶   2.5 × 10⁻⁶   5.29.1 12 15 183 0.3 2.0 0.05 0.1 5 × 10⁻⁵ 3 × 10⁻⁵ 1 × 10⁻⁵ 1 × 10⁻⁵ 4.39.0 20 30 184 0.3 2.0 0.05 0.1 1 × 10⁻⁴ 2 × 10⁻⁵ 4 × 10⁻⁵ 4 × 10⁻⁴ 4.19.1 22 30 185 0.3 2.0 0.05 0.1 1 × 10⁻³ 5 × 10⁻⁴ 3 × 10⁻⁴ 2 × 10⁻⁴ 3.08.7 23 30 186 0.3 2.0 0.05 0.1 1 × 10⁻² 5 × 10⁻³ 1 × 10⁻³ 4 × 10⁻³ 2.19.1 25 30 187 0.3 2.0 0.05 0.1 5 × 10⁻² 0  3 × 10⁻² 2 × 10⁻² 1.2 9.0 2830 188 0.3 2.0 0.05 0.1 0.5 0.3 0.1 0.1 1.1 9.3 29 30 * 189 0.3 2.0 0.050.1 1  0.5 0.3 0.2 0.4 9.2 29 30

As can be seen from Table 8, in the samples containing Ga instead of Al,when the content of Ga was set in the range of from 2×10⁻⁵ to 0.5 atompercent (sample Nos. 138 to 143 and 145 to 158), although the varistorvoltage was low, such as approximately 9 V, the superior propertiescould be obtained, that is, the initial insulation resistance IR was 1.0MΩ or more, the surge resistance was 20 A or more, and the ESDresistance was 30 kV.

As can be seen from Table 9, instead of Al and Ga, when the content ofIn was set in the range of from 2×10⁻⁵ to 0.5 atom percent (sample Nos.160 to 165 and 167 to 180), as was the case described above, althoughthe varistor voltage was low, such as approximately 9 V, the initial IRwas 1.0 MΩ or more, the surge resistance was 20 A or more, and the ESDresistance was 30 kV.

Furthermore, as can be seen from Table 10, in the case in which Al, Ga,and In were optionally combined with each other, when the total contentwas set in the range of from 2×10⁻⁵ to 0.5 atom percent (sample Nos. 183to 188), as was the case described above, although the varistor voltagewas low, such as approximately 9 V, the initial IR was 1.0 MΩ or more,the surge resistance was 20 A or more, and the ESD resistance was 30 kV.

From the results shown in Tables 7 to 10, when at least one of Al, Ga,and In was contained at a total content in the range of from 2×10⁻⁵ to0.5 atom percent, in a multilayer varistor designed to cooperate with acircuit driven at a low voltage, such as a rated voltage of 30 V orless, the leak current could be decreased, and a high surge resistanceand a high ESD resistance could be realized. In addition, when thevaristor voltage was low, such as approximately 9 V, an initial IR of1.0 MΩ or more, a surge resistance of 20 A or more, an ESD resistance of30 kV could be obtained.

Example 5

While the contents of Pr, Co, K, and Al used as a sub-component werefixed constant, the content of Zr was changed. Green sheets havingcompositions of composition Nos. 1 to 13 shown in Table 11 were used.Multilayer varistors were formed in the same manner as that in Example 1except that the thicknesses of the green sheets were adjusted to be 25,35, and 42 μm before firing, and that the varistor voltages were set toapproximately 9, 12, and 27 V, and subsequently, the evaluation wasperformed. The results are shown in Table 12 below. TABLE 11 COMPOSITIONADDITION ELEMENT (atom %) NO. Pr Co K Al Zr * 1 0.3 2 0.05 1 × 10⁻⁴0.000001 * 2 0.3 2 0.05 1 × 10⁻⁴ 0.0001 * 3 0.3 2 0.05 1 × 10⁻⁴ 0.001 40.3 2 0.05 1 × 10⁻⁴ 0.005 5 0.3 2 0.05 1 × 10⁻⁴ 0.01 6 0.3 2 0.05 1 ×10⁻⁴ 0.05 7 0.3 2 0.05 1 × 10⁻⁴ 0.1 8 0.3 2 0.05 1 × 10⁻⁴ 1 9 0.3 2 0.051 × 10⁻⁴ 3 10 0.3 2 0.05 1 × 10⁻⁴ 5 * 11 0.3 2 0.05 1 × 10⁻⁴ 6 * 12 0.32 0.05 1 × 10⁻⁴ 8 * 13 0.3 2 0.05 1 × 10⁻⁴ 10

TABLE 12 THICKNESS OF SURGE ESD SAMPLE COMPOSITION CHARACTERISTICVARISTOR RESIS- RESIS- NO. NO. LAYER INITIAL IR VOLTAGE TANCE TANCE *190 1 25 μm 0.8 MΩ 8.8 V 18 A 2 kV * 191 2 25 μm 1.2 MΩ 8.9 V 19 A 2kV * 192 3 25 μm 1.3 MΩ 9.1 V 20 A 5 kV 193 4 25 μm 1.5 MΩ 9.4 V 21 A 15kV 194 5 25 μm 1.8 MΩ 9.4 V 25 A 15 kV 195 6 25 μm 1.7 MΩ 9.1 V 24 A 30kV 196 7 25 μm 1.8 MΩ 9.4 V 25 A 30 kV 197 8 25 μm 1.6 MΩ 8.7 V 22 A 30kV 198 9 25 μm 2.0 MΩ 8.8 V 22 A 30 kV 199 10 25 μm 3.0 MΩ 9.1 V 20 A 30kV * 200 11 25 μm 3.2 MΩ 8.8 V 16 A 20 kV * 201 12 25 μm 3.3 MΩ 9.1 V 15A 10 kV * 202 13 25 μm 4.2 MΩ 9.4 V 12 A 2 kV * 203 1 35 μm 10 MΩ 11.7 V25 A 5 kV * 204 2 35 μm 20 MΩ 12.2 V 25 A 8 kV * 205 3 35 μm 22 MΩ 12.0V 30 A 15 kV 206 4 35 μm 30 MΩ 12.2 V 31 A 20 kV 207 5 35 μm 32 MΩ 12.2V 33 A 30 kV 208 6 35 μm 30 MΩ 12.0 V 35 A 30 kV 209 7 35 μm 30 MΩ 12.5V 35 A 30 kV 210 8 35 μm 31 MΩ 11.5 V 33 A 30 kV 211 9 35 μm 38 MΩ 12.1V 33 A 30 kV 212 10 35 μm 41 MΩ 12.1 V 30 A 30 kV * 213 11 35 μm 44 MΩ12.1 V 27 A 20 kV * 214 12 35 μm 45 MΩ 11.9 V 22 A 15 kV * 215 13 35 μm54 MΩ 12.5 V 21 A 5 kV * 216 1 42 μm 33 MΩ 26 V 46 A 5 kV * 217 2 42 μm41 MΩ 27.8 V 46 A 15 kV * 218 3 42 μm 50 MΩ 26.4 V 50 A 20 kV 219 4 42μm 58 MΩ 27.9 V 53 A 30 kV 220 5 42 μm 59 MΩ 27.1 V 53 A 30 kV 221 6 42μm 58 MΩ 27.1 V 54 A 30 kV 222 7 42 μm 61 MΩ 27.4 V 62 A 30 kV 223 8 42μm 64 MΩ 27.1 V 59 A 30 kV 224 9 42 μm 70 MΩ 27.3 V 55 A 30 kV 225 10 42μm 88 MΩ 26.7 V 51 A 30 kV * 226 11 42 μm 85 MΩ 27.1 V 47 A 20 kV * 22712 42 μm 82 MΩ 27.5 V 41 A 20 kV * 228 13 42 μm 100 MΩ 27.9 V 28 A 5 kV

As can be seen from Table 12, according to sample Nos. 219 to 225 of thepresent invention among the samples using a ceramic green sheet 42 μmthick, the varistor voltage V_(1mA) was in the range of from 26 to 28 V,and a circuit driven at a low voltage, such as a rated voltage of 30 Vor less, could be used; however, the initial IR was high, such as 50 MΩor more. In addition, the surge resistance was 50 A or more, and the ESDresistance was 30 kV. Hence, it was understood that very superiorproperties could be obtained.

On the other hand, according to sample Nos. 216, 217, 218, and 226 to228 having a Zr content outside the range of from 0.005 to 5.0 atompercent, the ESD resistance was 20 kV or less. Accordingly, when the Zrcontent was set in the range of from 0.005 to 5.0 atom percent, in amultilayer varistor designed to cooperate with a circuit driven at a lowvoltage, such as a rated voltage of 30 V or less, it was understood thatthe leak current could be decreased, and a high surge resistance and ahigh ESD resistance could be realized.

In addition, as can be seen from the results of sample Nos. 193 to 199and 206 to 212, in order to cooperate with a circuit driven at a lowervoltage, even when samples of green sheets 35 and 25 μm thick were usedso as to obtain a varistor voltage of 12 V or 9 V, it was understoodthat a multilayer varistor having a high initial IR and high ESDresistance could be obtained by the addition of Zr. However, when thecontent of Zr was 0.01 atom percent or less at a varistor voltage of 12V, and when the content of Zr was 0.05 atom percent or less at avaristor voltage of 9 V, the surge resistance and the ESD resistancewere liable to decrease.

FIGS. 5 to 7 are graphs each showing the relationship of the initial IRand the ESD resistance with respect to the Zr content of the individualsamples at varistor voltages of 9, 12, and 27 V. As can be seen fromTable 12 and FIGS. 5 to 7, when an appropriate amount of Zr was added toa composition containing ZnO as a primary component, Pr, Co, Al, and K,it was understood that the initial IR and the ESD resistance of amultilayer varistor designed to cooperate with a low voltage drivecircuit could be simultaneously improved.

Example 6

In Example 6, among Pr, Co, K, Al, and Zr used as a sub-component,samples in which the contents of Co and Al were primarily changed wereformed, and the properties thereof were evaluated.

Except that the contents of the sub-components were changed as shown inthe following Table 13, multilayer varistors were formed in the samemanner as that in Example 1, and the evaluation was performed. Theresults are shown in Table 13 below. TABLE 13 SURGE ESD SAMPLE ADDITIONELEMENT (atom %) INITIAL VARISTOR RESIS- RESIS- NO. Pr Co K Al Zr Co/AlIR VOLTAGE TANCE TANCE 229 0.3 2 0.05 2 × 10⁻⁵ 0.1 100000 4.2 MΩ 8.8 V20 A 30 kV 230 0.3 2 0.05 1 × 10⁻⁴ 0.1 20000 1.8 MΩ 8.7 V 25 A 30 kV 2310.3 2 0.05 5 × 10⁻⁴ 0.1 4000 1.7 MΩ 9.3 V 27 A 30 kV 232 0.3 2 0.05 1 ×10⁻³ 0.1 2000 1.3 MΩ 9.0 V 28 A 30 kV 233 0.3 2 0.05 5 × 10⁻³ 0.1 4001.2 MΩ 9.1 V 30 A 30 kV 234 0.3 2 0.05 1 × 10⁻² 0.1 200 1.0 MΩ 9.1 V 31A 30 kV 235 0.3 2 0.05 5 × 10⁻² 0.1 40 1.0 MΩ 9.3 V 33 A 30 kV 236 0.3 20.05 0.5 0.1 4 1.0 MΩ 9.6 V 34 A 30 kV 237 0.3 2.5 0.05 2 × 10⁻⁵ 0.1125000 4.3 MΩ 9.3 V 20 A 30 kV 238 0.3 2.5 0.05 1 × 10⁻³ 0.1 2500 2.9 MΩ9.1 V 26 A 30 kV 239 0.3 2.5 0.05 1 × 10⁻² 0.1 250 2.6 MΩ 8.8 V 28 A 30kV 240 0.3 2.5 0.05  0.05 0.1 50 2.6 MΩ 9.0 V 30 A 30 kV 241 0.3 2.50.05 0.1 0.1 25 2.3 MΩ 9.2 V 30 A 30 kV 242 0.3 2.5 0.05 0.5 0.1 5 1.9MΩ 8.8 V 31 A 30 kV 243 0.3 3 0.05 2 × 10⁻⁵ 0.1 150000 4.5 MΩ 8.9 V 23 A30 kV 244 0.3 3 0.05 1 × 10⁻³ 0.1 3000 3.0 MΩ 8.9 V 25 A 30 kV 245 0.3 30.05 1 × 10⁻² 0.1 300 2.8 MΩ 9.0 V 28 A 30 kV 246 0.3 3 0.05  0.05 0.160 2.3 MΩ 9.0 V 27 A 30 kV 247 0.3 3 0.05 0.1 0.1 30 2.4 MΩ 9.1 V 30 A30 kV 248 0.3 3 0.05 0.5 0.1 6 1.7 MΩ 9.0 V 31 A 30 kV 249 0.3 5 0.05 1× 10⁻⁴ 0.1 50000 2.7 MΩ 9.2 V 21 A 30 kV 250 0.3 5 0.05 1 × 10⁻³ 0.15000 2.6 MΩ 8.9 V 24 A 30 kV 251 0.3 5 0.05 1 × 10⁻² 0.1 500 2.6 MΩ 8.7V 26 A 30 kV 252 0.3 5 0.05  0.05 0.1 100 2.5 MΩ 8.8 V 29 A 30 kV 2530.3 5 0.05 0.1 0.1 50 2.2 MΩ 8.8 V 31 A 30 kV 254 0.3 5 0.05 0.5 0.1 101.9 MΩ 8.9 V 32 A 30 kV 255 0.3 10 0.05 1 × 10⁻⁴ 0.1 100000 4.1 MΩ 8.9 V20 A 30 kV 256 0.3 10 0.05 1 × 10⁻³ 0.1 10000 4.0 MΩ 8.8 V 24 A 30 kV257 0.3 10 0.05 1 × 10⁻² 0.1 1000 3.8 MΩ 9.1 V 26 A 30 kV 258 0.3 100.05  0.05 0.1 200 3.7 MΩ 9.2 V 29 A 30 kV 259 0.3 10 0.05 0.1 0.1 1003.6 MΩ 8.7 V 30 A 30 kV 260 0.3 10 0.05 0.5 0.1 20 3.0 MΩ 8.9 V 29 A 30kV

As can be seen from Table 13, although the contents of Co and Al weresimultaneously changed, when the changes were within the range of thepresent invention, the initial IR was 1.0 MΩ or more, the surgeresistance was 20 A or more, and the ESD resistance was 30 KV.

In particular, when the content of Co was set in the range of from 2.5to 10 atom percent, and the ratio of Co to Al was set so that Co/Al 20to 3,000 was satisfied, it was understood that more superior propertiescould be obtained, that is, an initial IR of 2.0 M0 MΩ or more and asurge resistance of 25 A or more could be obtained.

In the example, the contents of Co and Al were simultaneously changed;however, instead of Al, when Ga, In, or mixture of Al, Ga, and In wasadded, the same effect as described above could be obtained.

As described above, it is understood that a varistor, which can decreasethe leak current, can realize a high ESD resistance, and can be drivenat a low voltage, is obtained when ZnO is used as a primary component,and Pr, Co, K, Al, and Zr are used as sub-components. It is alsounderstood that when any one of the sub-components, Pr, Co, K, Al, andZr, is not used, a varistor cannot be obtained which can decrease theleak current, can realize a high ESD resistance, and can be driven at alow voltage. In addition, from the results shown in Tables 1 to 10, 12,and 13, when a ceramic composition is used containing ZnO as a primarycomponent and sub-components which includes Pr at a content of 0.05 to3.0 atomic percent of the total, Co at a content of 0.5 to 5.0 atompercent of the total, at least one of K, Na, and Li at a total contentof 0.005 to 0.5 atom percent of the total, at least one of Al, Ga, andIn at a total content of 2×10⁻⁵ to 0.5 atom percent of the total, and Zrat a content of 0.005 to 5.0 atom percent of the total, it is understoodthat a varistor can be obtained which can decrease the leak current, canrealize a high ESD resistance, and can be driven at a low voltage.

In addition to the ZnO used as a primary component and to the variouselements used as a sub-component, at least one type of element may alsobe used. Subsequently, this case will be described as Example 7.

Example 7

Except that the contents of Pr, Co, K, Al, and Zr were fixed constant,and that at least one of Ca, Sr, and Ba was contained as shown in thefollowing Table 14, multilayer varistors were formed in the same manneras that in Example 1, and the evaluation was performed. The results areshown in Table 14 below. TABLE 14 SURGE ESD INITIAL VARISTOR RESIS-RESIS- SAMPLE ADDITION ELEMENT (atom %) IR VOLTAGE TANCE TANCE NO. Pr CoK Al Zr Ca Sr Ba (MΩ) (V) (A) (kV) 261 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — —1.8 9.4 25 30 262 0.3 2.0 0.05 1 × 10⁻⁴ — — — — 0.8 8.8 18 2 263 0.3 2.00.05 1 × 10⁻⁴ 0.1 0.001 — — 2.2 8.8 25 30 264 0.3 2.0 0.05 1 × 10⁻⁴ 0.10.01 — — 2.5 8.7 25 30 265 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.05 — — 2.9 9.3 2430 266 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.1 — — 3.1 9.0 25 30 267 0.3 2.0 0.051 × 10⁻⁴ 0.1 0.3 — — 3.2 9.1 26 30 268 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.5 — —3.7 9.1 24 30 269 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.8 — — 4.3 9.3 25 30 2700.3 2.0 0.05 1 × 10⁻⁴ 0.1 1 — — 5.6 9.2 24 30 271 0.3 2.0 0.05 1 × 10⁻⁴0.1 2 — — 7.4 8.9 21 20 272 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 5 — — 9.2 8.9 1810 273 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.001 — 2.1 9.0 25 30 274 0.3 2.00.05 1 × 10⁻⁴ 0.1 — 0.01 — 2.6 9.0 24 30 275 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 —0.05 — 2.9 8.8 25 30 276 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.1 — 3.0 9.4 26 30277 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.3 — 3.3 9.2 26 30 278 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 — 0.5 — 3.6 8.9 25 30 279 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.8 — 4.69.0 24 30 280 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 1 — 5.1 9.1 23 30 281 0.3 2.00.05 1 × 10⁻⁴ 0.1 — 2 — 7.9 8.8 21 15 282 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — —0.001 2.0 8.9 25 30 283 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.01 2.5 9.1 24 30284 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.05 3.3 9.1 24 30 285 0.3 2.0 0.05 1× 10⁻⁴ 0.1 — — 0.1 3.4 9.0 23 30 286 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.33.5 9.3 25 30 287 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.5 3.5 8.8 24 30 2880.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.8 4.6 8.9 23 30 289 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 — — 1 5.2 8.8 25 30 290 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 2 7.8 9.020 15 291 0.3 2.0 0.05 0.1 0.005 — — — 2.3 9.1 25 30 292 0.3 2.0 0.050.1 0.01 — — — 2.4 8.8 25 30 293 0.3 2.0 0.05 0.1 0.1 — — — 2.9 9.0 2430 294 0.3 2.0 0.05 0.1 0.5 — — — 4.1 9.2 25 30 295 0.3 2.0 0.05 0.1 1 —— — 5.4 9.0 23 30 296 0.3 2.0 0.05 0.1 2 — — — 7.9 9.1 20 30

Sample No. 261 corresponds to sample No. 6 shown in Table 1. Sample No.262 corresponds to a conventionally known multilayer varistor.

As can be seen from Table 14, it was understood that when at least oneof Ca, Sr, and Ba was further contained, the IR could be improved. Inthis case, as can be seen from sample Nos. 263 to 270, 273 to 280, 282to 289, and 291 to 295, it was understood that when the total contentwas 1.0 atom percent or less, the initial IR could be effectivelyimproved. When the total content of Ca, Sr, and Ba was more than 1.0atom percent (sample Nos. 271, 272, 281, 290, and 296), although theinitial IR was further improved, the ESD resistance was decreased.

Example 8

Except that the contents of Pr, Co, K, Al, and Zr were fixed constant,and that at least one of LaNd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Ywas contained, multilayer varistors were formed from sintered bodieshaving sub-component compositions of sample Nos. 297 to 360 shown inTable 15 in the same manner as that in Example 1, and the evaluation wasperformed. In this example, sample No. 297 corresponds to sample No. 6shown in Table 1.

In addition, except that the contents of Pr, Co, K, Al, and Zr werefixed constant, and that Ca and La, Sr and La, Ba and La, or Ca, Sr, Ba,and La were contained so that the contents shown in Table 16 wereobtained, multilayer varistors of sample Nos. 361 to 384 were formed inthe same manner as that in Example 1, and the evaluation was performed.The results are shown in Table 15-1 and 15-2. TABLE 15-1 SURGE ESDSAMPLE ADDITION ELEMENT (atom %) VARISTOR RESIS- RESIS- NO. Pr Co K AlZr TYPE CONTENT INITIAL IR VOLTAGE TANCE TANCE 297 0.3 2.0 0.05 1 × 10⁻⁴0.1 — — 1.8 MΩ 8.8 V 25 A 30 kV 298 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 La 0.005 2MΩ 8.9 V 27 A 30 kV 299 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 La 0.01 2.2 MΩ 9.0 V31 A 30 kV 300 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 La 0.05 2.2 MΩ 9.1 V 35 A 30 kV301 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 La 0.1 2.3 MΩ 9.2 V 32 A 30 kV 302 0.3 2.00.05 1 × 10⁻⁴ 0.1 La 0.5 2.1 MΩ 8.8 V 31 A 30 kV 303 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 La 1 2.3 MΩ 8.9 V 27 A 30 kV 304 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 La 23.0 MΩ 9.1 V 21 A 20 kV 305 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 La 5 3.2 MΩ 9.0 V19 A 10 kV 306 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Nd 0.005 2.2 MΩ 9.0 V 27 A 30kV 307 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Nd 0.01 2.5 MΩ 8.9 V 32 A 30 kV 308 0.32.0 0.05 1 × 10⁻⁴ 0.1 Nd 0.5 2.6 MΩ 8.8 V 33 A 30 kV 309 0.3 2.0 0.05 1× 10⁻⁴ 0.1 Nd 1 2.6 MΩ 9.3 V 27 A 30 kV 310 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Nd5 3.1 MΩ 9.2 V 21 A 20 kV 311 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Sm 0.005 1.9 MΩ9.2 V 25 A 30 kV 312 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Sm 0.01 2.1 MΩ 8.9 V 33 A30 kV 313 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Sm 0.5 3.0 MΩ 9.1 V 34 A 30 kV 3140.3 2.0 0.05 1 × 10⁻⁴ 0.1 Sm 1 3.1 MΩ 9.1 V 27 A 30 kV 315 0.3 2.0 0.051 × 10⁻⁴ 0.1 Sm 5 3.4 MΩ 9.1 V 22 A 15 kV 316 0.3 2.0 0.05 1 × 10⁻⁴ 0.1Eu 0.005 2.3 MΩ 9.1 V 26 A 30 kV 317 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Eu 0.012.9 MΩ 9.0 V 33 A 30 kV 318 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Eu 0.5 3.0 MΩ 8.9V 31 A 30 kV 319 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Eu 1 3.5 MΩ 9.2 V 29 A 30 kV320 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Eu 5 3.9 MΩ 9.3 V 23 A 20 kV 321 0.3 2.00.05 1 × 10⁻⁴ 0.1 Gd 0.005 2.0 MΩ 9.0 V 28 A 30 kV 322 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 Gd 0.01 2.2 MΩ 9.1 V 31 A 30 kV 323 0.3 2.0 0.05 1 × 10⁻⁴ 0.1Gd 0.5 2.3 MΩ 9.0 V 33 A 30 kV 324 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Gd 1 2.6 MΩ9.3 V 28 A 30 kV 325 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Gd 5 2.9 MΩ 9.1 V 23 A 15kV 326 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tb 0.005 2.5 MΩ 8.8 V 27 A 30 kV 3270.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tb 0.01 2.9 MΩ 8.7 V 33 A 30 kV 328 0.3 2.00.05 1 × 10⁻⁴ 0.1 Tb 0.5 3.3 MΩ 8.8 V 35 A 30 kV 329 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 Tb 1 3.5 MΩ 9.3 V 28 A 30 kV 330 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tb 53.9 MΩ 9.0 V 21 A 15 kV

TABLE 15-2 SURGE ESD SAMPLE ADDITION ELEMENT (atom %) VARISTOR RESIS-RESIS- NO. Pr Co K Al Zr TYPE CONTENT INITIAL IR VOLTAGE TANCE TANCE 3310.3 2.0 0.05 1 × 10⁻⁴ 0.1 Dy 0.005 2.5 MΩ 9.2 V 27 A 30 kV 332 0.3 2.00.05 1 × 10⁻⁴ 0.1 Dy 0.01 2.3 MΩ 9.1 V 33 A 30 kV 333 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 Dy 0.5 2.9 MΩ 9.0 V 34 A 30 kV 334 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Dy1 3.2 MΩ 8.8 V 29 A 30 kV 335 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Dy 5 3.2 MΩ 8.8V 24 A 20 kV 336 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Ho 0.005 2.3 MΩ 8.9 V 26 A 30kV 337 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Ho 0.01 2.4 MΩ 9.0 V 30 A 30 kV 338 0.32.0 0.05 1 × 10⁻⁴ 0.1 Ho 0.5 2.9 MΩ 8.8 V 31 A 30 kV 339 0.3 2.0 0.05 1× 10⁻⁴ 0.1 Ho 1 3.0 MΩ 8.9 V 28 A 30 kV 340 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Ho5 3.3 MΩ 9.0 V 23 A 20 kV 341 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Er 0.005 2.1 MΩ9.1 V 27 A 30 kV 342 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Er 0.01 2.8 MΩ 8.8 V 33 A30 kV 343 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Er 0.5 2.7 MΩ 9.1 V 35 A 30 kV 3440.3 2.0 0.05 1 × 10⁻⁴ 0.1 Er 1 3.1 MΩ 9.2 V 28 A 30 kV 345 0.3 2.0 0.051 × 10⁻⁴ 0.1 Er 5 3.0 MΩ 9.0 V 21 A 20 kV 346 0.3 2.0 0.05 1 × 10⁻⁴ 0.1Tm 0.005 2.1 MΩ 8.8 V 27 A 30 kV 347 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tm 0.012.4 MΩ 8.9 V 33 A 30 kV 348 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tm 0.5 2.9 MΩ 9.1V 34 A 30 kV 349 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tm 1 3.0 MΩ 9.0 V 29 A 30 kV350 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Tm 5 3.3 MΩ 9.1 V 23 A 20 kV 351 0.3 2.00.05 1 × 10⁻⁴ 0.1 Yb 0.005 1.9 MΩ 9.0 V 28 A 30 kV 352 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 Yb 0.01 2.2 MΩ 8.8 V 33 A 30 kV 353 0.3 2.0 0.05 1 × 10⁻⁴ 0.1Yb 0.5 2.5 MΩ 8.9 V 35 A 30 kV 354 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Yb 1 2.6 MΩ9.2 V 29 A 30 kV 355 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Yb 5 2.8 MΩ 9.1 V 23 A 20kV 356 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Y 0.005 1.9 MΩ 9.0 V 29 A 30 kV 357 0.32.0 0.05 1 × 10⁻⁴ 0.1 Y 0.01 2.1 MΩ 8.9 V 35 A 30 kV 358 0.3 2.0 0.05 1× 10⁻⁴ 0.1 Y 0.5 2.3 MΩ 8.8 V 36 A 30 kV 359 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Y1 2.4 MΩ 8.7 V 29 A 30 kV 360 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 Y 5 2.8 MΩ 8.9 V24 A 20 kV

TABLE 16 SURGE ESD INITIAL VARISTOR RESIS- RESIS- SAMPLE ADDITIONELEMENT (atom %) IR VOLTAGE TANCE TANCE NO. Pr Co K Al Zr Ca Sr Ba La(MΩ) (V) (A) (kV) 361 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.001 — — 0.005 2.4 8.827 30 362 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.01 — — 0.01 2.7 8.9 31 30 363 0.32.0 0.05 1 × 10⁻⁴ 0.1 0.1 — — 0.05 3.2 9.0 35 30 364 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 0.5 — — 0.1 3.9 9.1 32 30 365 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.8 — —0.5 4.4 9.2 31 30 366 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 1 — — 1 5.6 8.8 27 30367 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.001 — 0.005 2.3 9.2 26 30 368 0.3 2.00.05 1 × 10⁻⁴ 0.1 — 0.01 — 0.01 2.7 8.9 32 30 369 0.3 2.0 0.05 1 × 10⁻⁴0.1 — 0.1 — 0.05 3.4 8.9 34 30 370 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.5 — 0.13.8 8.9 35 30 371 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 0.8 — 0.5 4.5 9.1 35 30372 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — 1 — 1 5.4 8.9 29 30 373 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 — — 0.001 0.005 2.1 9.0 28 30 374 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — —0.01 0.01 2.5 9.0 32 30 375 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.1 0.05 3.29.1 36 30 376 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.5 0.1 4.2 9.2 35 30 3770.3 2.0 0.05 1 × 10⁻⁴ 0.1 — — 0.8 0.5 5.0 8.9 34 30 378 0.3 2.0 0.05 1 ×10⁻⁴ 0.1 — — 1 1 5.4 9.0 26 30 379 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.00050.0003 0.002 0.005 2.5 9.1 27 30 380 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.0050.002 0.003 0.01 2.8 8.8 30 30 381 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.01 0.050.04 0.05 3.1 8.9 36 30 382 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.2 0.2 0.1 0.14.4 8.9 35 30 383 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.4 0.4 0.2 0.5 4.5 9.2 3330 384 0.3 2.0 0.05 1 × 10⁻⁴ 0.1 0.4 0.4 0.2 1 4.8 9.0 29 30

As can be seen from Table 15, according to sample Nos. 298 to 303, 306to 309, 311 to 314, 316 to 319, 321 to 324, 326 to 329, 331 to 334, 336to 339, 341 to 344, 346 to 349, 351 to 354, and 356 to 359, whichcontained at least one of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,and Y, the surge resistance was further improved, and according tosample Nos. 299 to 302, 307, 308, 312, 313, 317, 318, 322, 323, 327,328, 332, 333, 337, 338, 342, 343, 347, 348, 352, 353, 357, and 358,which contained at least one of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, and Y at a content in the range of from 0.01 to 0.5 atom percent, itwas understood that the surge resistance could be even further improved.However, according to sample Nos. 304, 305, 310, 315, 320, 325, 330,335, 340, 345, 350, 355, and 360, which contained at least one of La,Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y at a content of more than1.0 atom percent, it was understood that the surge resistance and theESD resistance were adversely decreased.

As can be seen from Table 16, according to sample Nos. 361 to 366 whichused a sintered body further containing Ca and La, it was understoodthat the IR and the surge resistance were even further improved. Inaddition, as can be seen from Table 16, it was understood that thecontent of Ca was preferably set to 1.0 atom percent or less, and thatthe content of La was preferably set to 1.0 atom percent or less.

As can be seen from Table 16, according to sample No. 367 to 372 furthercontaining Sr and La, it was understood that the IR and the surgeresistance were even further improved. In addition, in particular,according to sample No. 368 to 370 in which La was contained at acontent in the range of from 0.01 to 0.5 atom percent, it was understoodthe surge resistance could be even further improved.

As can be seen from the results according to sample Nos. 373 to 378,when a sintered body further containing Ba and La was used, it wasunderstood that the IR and the surge resistance could be even furtherimproved. In particular, according to sample No. 374 to 376 in which theLa content was in the range of from 0.01 to 0.5 atom percent, it wasunderstood that the surge resistance was even further improved.

According to sample Nos. 379 to 384, since Ca, Sr, Ba, and La werecontained as shown in Table 16, it was understood that the IR and thesurge resistance could be even further improved. In addition, inparticular, according to sample Nos. 381 to 383 in which the La contentwas in the range of from 0.01 to 0.5 atom percent, it was understood thesurge resistance could be even further improved.

As described above, since the ceramic composition for a varistor,according to the examples, comprises zinc oxide as a primary componentand sub-components including at least one of Pr, Co, K, Na, and Li, atleast one of Al, Ga, and In, and Zr at specific contents describedabove, a varistor can be provided which has a small leak current and ahigh ESD resistance and which is preferably driven at a low voltage.

Industrial Applicability

As has thus been described, the ceramic composition for a varistor,according to the present invention, is used for manufacturing a varistorpreferably used for an electrostatic protection element or a noisefilter, and in particular, is preferably used for manufacturing amultilayer varistor composed of a plurality of varistor layers laminatedto each other.

1-7. (canceled)
 8. A ceramic composition utilizable to form a varistor,comprising: zinc oxide as a primary component; and sub-componentscomprising praseodymium at a content of 0.05 to 3.0 atomic percent ofthe total, cobalt at a content of 0.5 to 10 atom percent of the total,at least one of potassium, sodium and lithium at a total content of0.005 to 0.5 atom percent of the total, at least one of aluminum,gallium and indium at a total content of 2×10⁻⁵ to 0.5 atom percent ofthe total, and zirconium at a content of 0.005 to 5.0 atom percent ofthe total.
 9. The ceramic composition according to claim 8, furthercomprising at least one of calcium, strontium and barium at a totalcontent of 1.0 atom percent or less of the total.
 10. The ceramiccomposition for a varistor, according to claim 9, further comprising atleast one member selected from the group consisting of lanthanum,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, thulium, ytterbium and yttrium at a total content of 1.0 atompercent or less of the total.
 11. The ceramic composition according toclaim 10, wherein said at least one member is La.
 12. The ceramiccomposition according to claim 8, wherein the zirconium is contained ata content of from 0.01 to 5.0 atom percent of the total.
 13. The ceramiccomposition according to claim 12, wherein the zirconium is contained ata content of from 0.05 to 5.0 atom percent of the total.
 14. The ceramiccomposition according to claim 8, further comprising at least one memberselected from the group consisting of lanthanum, neodymium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium and yttrium at a total content of about 1 atom percent or lessof the total.
 15. The ceramic composition according to claim 14, whereinsaid at least one member is at a total content of 0.01 to 0.5 atompercent of the total.
 16. The ceramic composition according to claim 14,wherein said at least one member is La.
 17. The ceramic compositionaccording to claim 8, containing cobalt and aluminum at an atomic ratioof 20 to 3,000.
 18. The ceramic composition according to claim 17,wherein said at least one of potassium, sodium and lithium is potassium,and the zirconium is contained at a content of from 0.01 to 5 atompercent of the total.
 19. The ceramic composition according to claim 8,wherein said at least one of potassium, sodium and lithium is potassium.20. A varistor comprising a sintered body of sintered ceramiccomposition and a plurality of terminal electrodes on exterior surfacesof the sintered body, the ceramic composition sintered comprising zincoxide as a primary component and sub-components which comprisepraseodymium at a content of 0.05 to 3.0 atomic percent of the total,cobalt at a content of 0.5 to 10 atom percent of the total, at least oneof potassium, sodium and lithium at a total content of 0.005 to 0.5 atompercent of the total, at least one of aluminum, gallium and indium at atotal content of 2×10⁻⁵ to 0.5 atom percent of the total, and zirconiumat a content of 0.005 to 5.0 atom percent of the total.
 21. The varistoraccording to claim 20, wherein the ceramic composition sintered contains(a) at least one of calcium, strontium and barium at a total content of1 atom percent or less of the total, (b) at least one member selectedfrom the group consisting of lanthanum, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium andyttrium at a total content of 1 atom percent or less of the total, or(c) both (a) and (b).
 22. The varistor according to claim 20, whereinthe zirconium is contained at a content of from 0.01 to 5 atom percentof the total.
 23. The varistor according to claim 20, wherein theceramic composition sintered contains containing cobalt and aluminum atan atomic ratio of 20 to 3,000, said at least one of potassium, sodiumand lithium is potassium, and the zirconium is contained at a content offrom 0.01 to 5 atom percent of the total.
 24. The varistor according toclaim 23, further comprising a plurality of electrodes in the interiorof the sintered body such that each adjacent pair of electrodes in saidplurality of internal electrodes is disposed with a layer of sinteredbody provided therebetween and each of said internal electrodes iselectrically connected to an exterior electrode.
 25. The varistoraccording to claim 22, further comprising a plurality of electrodes inthe interior of the sintered body such that each adjacent pair ofelectrodes in said plurality of internal electrodes is disposed with alayer of sintered body provided therebetween and each of said internalelectrodes is electrically connected to an exterior electrode.
 26. Thevaristor according to claim 21,further comprising a plurality ofelectrodes in the interior of the sintered body such that each adjacentpair of electrodes in said plurality of internal electrodes is disposedwith a layer of sintered body provided therebetween and each of saidinternal electrodes is electrically connected to an exterior electrode.27. The varistor according to claim 20, further comprising a pluralityof electrodes in the interior of the sintered body such that eachadjacent pair of electrodes in said plurality of internal electrodes isdisposed with a layer of sintered body provided therebetween and each ofsaid internal electrodes is electrically connected to an exteriorelectrode.